Depression is a disease which shows a typical condition of suppressed mood among mood disorders, and one of its causes is considered to be functional disorders in the central serotonergic and noradrenergic nervous systems. Serotonin and noradrenaline are decomposed and metabolized by monoamine oxidases (mainly by type A-monoamine oxidase) to lose their biological activities. Type A-monoamine oxidase inhibitors are considered to be useful as antidepressants and such inhibitors have been studied and developed intensively. Recently, Moclobernide has been supplied clinically as a selective type A-monoamine oxidase inhibitor.